UNIVERSITY  OF  CALIFORNIA         Agricultural  Experiment  Station 

COLLEGE    OF    AGRICULTURE  ^ENJ.    IDE    WHEELER,    Pres.dent 

THOMAS    FORSYTH     HUNT,    DCAN  AND    DIRECTOR 

BERKELEY 

CIRCULAR  No.  101 
(June,  1913) 

CODLING  MOTH  CONTROL  IN  THE 
SACRAMENTO  VALLEY 

BY 

C.  W.  WOODWORTH 


The  investigation  by  this  Station  of  the  problem  of  preventing 
wormy  apples  or  pears  has  been  condncted  chiefly  in  the  great  apple 
section  of  this  state,  the  Pajaro  Valley.  Dnring  the  summer  of  1911 
Mr.  L.  J.  Nickels,  an  assistant  in  the  Entomological  Department  was 
given  opportunity,  through  the  cooperation  of  Mr.  H.  P.  Stabler, 
Horticultural  Commissioner  of  Sutter  County,  to  compare  the  life 
history  of  the  insect  in  that  region.  A  detailed  account  of  this  investi- 
gation is  soon  to  be  published. 

LIFE  HISTORY 

In  striking  contrast  with  the  conditions  prevailing  in  the  Pajaro 
Valley  the  moths  appear  early  in  spring  and  are  ready  to  begin  to  laj^ 
their  eggs  before  the  petals  have  fallen  from  the  blossoms.  Egg  laying 
is  concluded  in  about  a  month. 


Fig.  1. — Newly -hatched  codling  moth 
larva  crawling  between  the  stamens  in 
the  blossom  cup  of  apple,  also  young 
woolly   aphis. 


Fig.  2. — Surface  feeding  by  young 
codling  moth  larvae,  a,  b,  c,  successive 
feedings. 


Fig.  3. — Section  through  the  same 
spot   as   figure   2. 


The  eggs  are  flat,  transparent,  cemented  fast  to  the  surface  of  the 
leaves  or  fruit  and  about  the  size  of  a  pin  head.  They  are  so  incon- 
spicuous as  to  be  difficult  to  find.  Eggs  hatch  in  about  81/2  days  and 
the  young  larvae  are  abundant  in  the  apples  by  the  time  they  are  as 
large  as  peas.  The  young  worm  first  makes  a  burrow,  not  eating  the 
fruit,  but  biting  off  bits,  which  it  uses  in  making  a  canopy  over  the 
entrance,  binding  these  fragments  together  with  silk.  After  establish- 
ing itself  within  the  fruit  the  worm  begins  to  feed  both  within  the 
burrow  and  on  the  surface,  and  continues  to  live  just  beneath  the  skin 
for  several  days,  finally  burrowing  deep  into  the  fruit.  In  all  a  little 
less  than  a  month  (average  27  days)  is  spent  within  the  fruit.  Upon 
leaving  the  fruit  the  worm  proceeds  to  spin  a  tough  silken  cocoon  in 
some  crevice  and  remains  another  month  within  this  protection  chang- 
ing into  a  pupa  and  finally  emerging  as  a  moth,  completing  a  full 
generation  by  the  middle  or  latter  part  of  July,  some  individuals 
developing  more  rapidly  and  others  taking  considerably  longer. 

A  second  generation  occupies  August  and  September  and  a  few  of 
the  more  precocious  are  able  to  produce  a  third  generation  in  the  fall. 
Usually  the  worms  of  the  second  generation  go  into  hibernation  as  soon 
as  they  have  spun  their  cocoons  and  do  not  transform  till  the  follow- 
ing spring. 

FRUIT  AFFECTED 

Apples. — Most  of  the  apples  grown  in  the  Sacramento  Valley  are 
early  fruit  which  is  ready  to  harvest  early  enough  to  escape  the  attack 
of  the  second  brood  of  worms.  Where  nothing  is  done  to  protect  the 
fruit  the  worms  injure  but  two-thirds  of  the  crop.  If  the  orchard 
were  isolated  and  all  fruit  removed  at  this  time,  the  second  generation 
might  be  largely  annihilated  by  starvation. 

Pears,  are  very  much  more  largely  grown  in  the  Sacramento  Valley 
than  is  the  apple  and  is  not  usually  seriously  affected  by  the  first  brood 
of  worms  (less  than  10  per  cent)  but  if  not  controlled  the  worms  of 
the  second  generation  injure  a  third  of  the  crop.  The  usual  method 
of  harvesting  pears  removes  the  larger  proportion  of  the  worms  of  this 
second  generation  from  the  orchard,  hence  the  relatively  small  injury 
from  the  first  generation  of  the  following  spring. 

THEORY  OP  CONTROL 

The  gathering  and  destruction  of  fallen  fruit  was  at  one  time 
required  by  law  in  California.  The  placing  of  bands  made  of  old 
grain  sacks  around  the  trunk  and  examining  them  once  a  week  or 


once  in  two  weeks  was  found  to  enable  the  grower  to  destroy  more 
of  the  worms  than  by  gathering  the  fruit  and  was  the  chief  depend- 
ence in  this  state  a  score  of  years  ago. 

A  parasitic  wasp  was  imported  from  Spain  which  feeds  on  the 
insect  but  this  proved  of  no  practical  value. 

The  use  of  arsenical  poisons  has  coma  to  be  the  sole  method  for 
the  control  of  this  insect.  By  their  use  the  insects  are  killed  before 
instead  of  after  the  danger  is  done  and  the  loss  can  be  reduced  to 
the  neighborhood  of  one  per  cent  and  sometimes  the  destruction  seems 
to  be  complete.  At  first  it  was  thought  that  the  poison  could  not 
affect  an  insect  like  this  that  bores  deep  into  the  fruit.  When  experi- 
ments proved  that  the  poisons  did  protect  the  crop  the  general  belief 
changed  to  the  idea  that  they  got  the  poison  in  the  process  of  burrow- 
ing through  the  skin.  The  fact  noted  above  that  they  do  not  swallow 
the  tissue  removed  in  this  process  suggests  that  the  subsequent  surface 
feeding  is  the  fatal  operation. 

The  fact  was  early  observed  that  in  some  regions  the  worm  enters 
the  fruit  chiefly  at  the  blossom  end,  giving  rise  to  the  erroneous  idea 
that  the  eggs  were  laid  at  that  point.  It  is  a  very  general  belief  that 
poison  must  be  deposited  within  the  cup  to  prevent  the  entrance  of 
the  worms,  and  in  most  varieties  of  apples  this  can  only  be  done  during 
the  fortnight  following  the  dropping  of  the  petals.  In  the  Pajaro 
valley  it  was  observed  that  the  great  majority  enter  the  fruit  else- 
where and  in  Sutter  county  only  a  third  of  the  worms  entered  at  this 
place.  Furthermore,  it  was  noticed  that  spraying  was  completely 
effective  in  the  Pajaro  valley  when  applied  long  after  the  calyx  is 
closed  and  in  the  Sacramento  valley  good  results  followed  when  only 
two  or  three  per  cent  of  the  cups  showed  an  appreciable  amount  of 
the  spray.  In  both  of  these  cases  the  decrease  of  those  entering  the 
blossom  end  was  practically  as  great  as  of  those  entering  on  the  side. 

It  will  thus  be  seen  that  we  do  not  know  enough  of  the  facts  to 
explain  the  reasons  for  the  efficiency  of  the  poison. 


METHOD  OF  CONTROL 

All  who  have  investigated  the  subject  agree  that  the  poison  must 
be  applied  before  the  worms  enter  the  fruit  and  that  a  thorough 
application  is  necessary  for  the  best  results.  Both  the  life  history 
and  observations  of  the  results  of  practical  spraying  work  indicate 
that  the  time  for  the  first  application  in  that  valley  is  as  soon  as 
possible  after  the  petals  fall. 


4 

In  the  case  of  pears  or  fall  apples,  unless  this  first  spraying  has 
been  very  thorough,  the  second  brood  will  also  need  attention  the  latter 
part  of  July  or  early  in  August.  The  placing  of  bands  of  sacking 
about  a  few  of  the  trees  is  advised  as  a  means  of  keeping  track  of 
the  appearance  of  the  second  crop.  These  should  be  examined  about 
the  1st  and  15th  of  July  aud  August. 

One  thorough  spraying  for  summer  apples  and  one  or  two  for  fall 
apples  and  pears  will  completely  control  the  codling  moth  in  the 
Sacramento  Valley. 

AMOUNT  TO  USE 

For  a  single  medium-sized  tree: 

Lead  Arsenate i/^  pint 

Water 5  gallons 

For  Orchards  use: 

Lead  Arsenate   3-6  lbs. 

Water   100  gallons 

This  is  enough  for  about  a  quarter  of  an  acre  of  average  sized 
trees.  Instead  of  Lead  Arsenate  one  can  substitute  Zinc  Arsenite, 
using  only  one-third  as  much  (1-2  lbs.  for  100  gallons)  or  Paris 
green,  using  a  quarter  as  much  as  of  the  lead  (%-%  lbs.  to  100  gal- 
lons), in  the  latter  case  it  is  customary  to  add  about  three  times  as 
much  lime.  This  serves  two  purposes,  holding  the  arsenical  on  the  tree 
and  marking  the  tree  so  that  one  can  be  sure  of  the  thoroughness  of 
the  application. 


